Multiple-speed electric motor



H. M. NORMAN MULTIPLE SPEED ELECTRIC MOTOR Filed June 2, 1947 March 28, 1950 resented 1 uNiTED y .25mn

MULTIPLE-smv mc'rnrc Moron Horace lll. Norman, Skokie, IIL', assignor to Stewart-W Y corporation of Appueauen .time e, um, ne. 151,665

schim. (ci. aie-siii The present invention relates to electric motors and has for its primary object the provision of a vnew and improved multiple electric motor.

A further object ci the present invention is to provide a simple, eiiective, low cost multiple speed electric motor having good starting torque characteristics at all speeds.

A further object of the present invention is to provide a new and improved multiple speed electric motor of such a character that such motors can be built readily, and existing motors can be converted readily to provide the desired variable speeds.

Other objects and advantages of the present invention will become apparentl from the ensuing description oi' two embodimentsthereof,

in the course of which reference is had to thel Referring met te Fig. 1, the eleetrie motor `1s' illustrated as comprising an amature Il and a shunt field I2. The connection of these to the power supply, which may be a battery I 4, is controlled by speed selector switch means Il controlling the connections of the armature and eld to the battery through a power supply conductor IB having an on-oil.' switch 20 interposed therein.

The present invention is particularly adapted for installations where low cost is vital, as in electric windshield wipers. In an installation of this character the switch is the ignition switch, and the battery I4 is the usual automobile storage battery, one terminal of which is grounded through conductor 22, and the other connected to conductor I8 andswitch 20. The circuit to the battery from the motor is completed through a ground conductor 24 connected by conductor 20 to one terminal of the armature. and by conductor 2l to the corresponding termi- IAnal of the ileld.

The present invention, as already indicated, provides a simple, eilective and low cost means for operating the motor at a plurality of speeds. Thisvmeans includes resistance means, which is illustrated as being a single resistor II permanently connected to corresponding terminals of the ileld and armature by conductors 32 and 34, respectively. The connections of the resistor,

field and armature to the selector switch means it is such that for one speed the resistor Il is connected in series with the ileld, for another arncr Corporation, Chicago, Ill., a

, the resistor connected in Ser18-with armature, and for a` third speed the resistor. is

enectively not in circuit with either.

The selector switch means may be a simple plural position switch comprising a movable switch blade 36 illustrated as being in an oi!- sistor 3,0. In this position the ileld is connected directly across the `battery while the resistor fil is connected in series with the armature, thereby reducing the armature voltage.

In the intermediate speed position the switch blade engages contacts 4I and 42 which are connected by conductors 43 and 45 to conductors I2 and 34 and thus directly to terminals of the field and armature. In this position full battery voltage is applied to the eld and armature and the resistor 30 lis effectively not in circuit.

In the high speed position the switch blade It is in engagement with cantact 44 so that the full battery voltage is applied across the armature and a reduced voltage is applied to the field by virtue of the resistor 30 being inserted in series with the latter.

The resistor 30 can be placed either inside or outside of the motor. Ordinarily it will be placed inside of the motor. Its value in ohms can also be made relatively small because the desired speed differential, at least between the high and low speeds, is obtained by virtue of I using the resistance in series selectively with both the ileld and armature. Consequently, to obtain the high speed, the voltage applied to the iield does not have to be reduced as much as in conventional arrangements where the resistor is connected only in series with the field. The arrangement also produces a better high speed starting torque than is possible with conventional arrangements so that good torques are provided for the various speeds.

It is believed that the operation of the motor will -be apparent from the foregoing but it will be reviewed brley. The motor is placed into operation by closing the switch 20 and operating the movable switch blade 38 into a desired position. In the high speed position the bladerengages contact 44, with the result that the armature is operated at full voltage and the ileld at reduced voltage, thereby to provide the high speed operation. In the intermediate speed position the switch blade engages contacts 4I voltage and the armature at reduced voltage.-

YIt is-possible to use a single resistor in motors designed to embody thepresent invention. and it -4 is also possible touse a single resistor in the conversion of motors which have already been built ii' the amature land field resistances and the saturation curve of the magnetic circuit are :,soasss 4 f f ofsaids'witchtheamatureisdirectlyccnnected to said conductor and the. field-is connected to it through said iirstresistorand in another positionthei'leldisdirectlyconnectedtosailricon` ductor and the amature is connected to it v through the resistors connected in parallel.

2. 'A multiple speed electric motor including an armature, a field connected in shunt with the arvmature. a .resistor connected between one eld such as to enable the single resistor to be used.v

Where the characteristics are not such. the arrangementoiFig.2canbeused. m Referring now to Fig. 2, it may be noted that the arrangement is like that illustrated in Fig.'1 except that two resistors Il and l2` are used. Resistor til is connected in the same manner as .resistor I0. while resistor I2 is connected to resistor l0, preferably by connection thereof to conductor M. The other teminal oi resistor l2 is connected to a switch contact Il adapted to be engaged by the movable switch blade It simultaneously with the contact connected to one terminal `oi' the resistor", preferably the contact 4l. y

In essence, the difference between the'two arrangements is that a resistance means of one value is inserted in series with the ileld, and a different value resistance means is inserted in series with the armature. The values ofthese resistors can be chosen `,so that the motor will have the desired operating characteristics. Consequently, this embodiment is particularly susceptible for use in converting existing motors into multiple speed motors.

While the present invention has been described in connection with the specific details of two embodiments thereof, it should be understood that these details are not intended to be limitative oi the invention except in so far as set forth in the accompanying claims. 4

Having thus described my invention, what I claim as new'and desire to secure by Letters Patent is:

amature. a field connected in shunt with the armature, a resistor connected between one field terminal and-one armature terminal, the remaining terminals being connected together, a second resistor having one of its two terminals connected to the Junction of said first mentioned resistor and the armature, and a plural position speed selector switch adapted selectively to connect the junction of both said resistors and amature or the junction of said ilrst resistor and ileld and the second terminal of said second resistor to a power supply conductor, whereby in one position 45' 1. A multiple speed electric motor including an and one amature terminal, the remaining terminals being connected together, a second resistor having one terminal connected to the Junction of said ilrst mentioned resistor and the armature and a second terminal. and speed selector switch means adapted selectively to connect the-'Junction of both said resistors and armature. vthe Junction of said first resistor and field and the second terminal of said second resistor, or the Junctions oi said nrst resistor with both the ileld and armature toa power supply conductos'. whereby in one condition of said .switch means the amature is directly connected to said conductor andthe field is connected toit through said first resistor, in another condition the heid is directly connected to said conductor and the amature is connected to it through the resistors connected inparallel, and in a further condition both the field and amature are directly connected to said conductor.

'3. A multiple speed electric motor including an amature, a field connected in shunt with the amature. first resistance means-connected between one field terminal and one amature terminal the other field and armature terminals being connected together, other resistance means ,having one of its terminals connected to said first resistance means, and speed selector switch means adapted selectively to connect a power `supply conductor to either the other terminal o! said second resistance and first mentioned field teminal. or to the first mentioned ileld and armature terminals, or to the first mentioned amature terminal.

HORACE M. NORMAN.

Rrzrfnnrsrzcas CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 865,811 Powell Sept. 10, 1907 1,282,836 Horton Oct. 29, 1918 u FOREIGN PATENTS `Number Country v Date 17,137 GreatBritain of 1900 

